| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 1996: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 1995: ¥1,000,000 (Direct Cost: ¥1,000,000)
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| Research Abstract |
This study examined the adaptations of gall-forming aphids to the heterogeneity of the hostplants. In the Japanese elm, which is the hostplants of several gall-forming aphids of the Pemphigidae, there was a great variation in the budburst time between individual trees. The gall-forming aphids induce galls successfully when the nymphs hatch synchronously with the host budburst and stimulate developing leaves. On each host tree, stabilizing selection was acting on the hatching time. However, because optimal hatching time differed between host trees, the aphid population was subject to heterogeneous selection throughout a host population. Under this selective regime, two kinds of adaptations were found in gall-forming aphids. In a non-migratory aphid, Kaltenbachiella japonica, clones were adapted to individual host trees, with the result of genetic differentiation in egg-hatching time between host trees. On the other hand, the egg hatch of the migratory aphid, Tetraneura sp.was often asynchronous with the budburst of the host tree. Newly hatched nymphs were subject to heterogeneous selection on host trees with various budburst times. To determine the genetic basis of egg-hatching in this species, hatching time was compared between half-sib families. There was significant additive genetic variance in this trait. This suggests that heterogeneous selection on host trees, coupled with density-dependence on each host tree, maintained additive genetic variance in the hatching time. Furthermore, maternal effects affected hatching time. Such effects occurred when sexual females developed under low nutritional conditions. Small nymphs produced by small mothers hatched late and were likely to be selected out during the galling process. Thus, in the hatching time of gall-forming aphids, there was a great variance due to genetic diversity and maternal effects.
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